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This document deals with the characterization of porous materials having pore widths in the macropore range of 50 nm to 500 µm. In recent years, the development of advanced adsorbents and catalysts (e.g., monoliths having hierarchical pore networks) has brought about a renewed interest in macropore structures. Mercury intrusion--extrusion porosimetry is a well-established method, which is at present the most widely used for determining the macropore size distribution. However, because of the reservations raised by the use of mercury, it is now evident that the principles involved in the application of mercury porosimetry require reappraisal and that alternative methods are worth being listed and evaluated. The reliability of mercury porosimetry is discussed in the first part of the report along with the conditions required for its safe use. Other procedures for macropore size analysis, which are critically examined, include the intrusion of other non-wetting liquids and certain wetting liquids, capillary condensation, liquid permeation, imaging, and image analysis. The statistical reconstruction of porous materials and the use of macroporous reference materials (RMs) are also examined. Finally, the future of macropore analysis is discussed. [ABSTRACT FROM AUTHOR]

The analysis of the porosity of materials is an important and challenging field in analytical chemistry. The gas adsorption and mercury intrusion methods are the most established techniques for quantification of specific surface areas, but unfortunately, dry materials are mandatory for their applicability. All porous materials that contain water and other solvents in their functional state must be dried before analysis. In this process, care has to be taken since the removal of solvent bears the risk of an incalculable alteration of the pore structure, especially for soft materials. In the present paper, we report on the use of small-angle X-ray scattering (SAXS) as an alternative analysis method for the investigation of the micro and mesopores within cellulose beads in their native, i.e., water-swollen state; in this context, they represent a typical soft material. We show that even gentle removal of the bound water reduces the specific surface area dramatically from 161 to 109 m g in cellulose bead sample type MT50 and from 417 to 220 m g in MT100. Simulation of the SAXS curves with a bimodal pore size distribution model reveals that the smallest pores with radii up to 10 nm are greatly affected by drying, whereas pores with sizes in the range of 10 to 70 nm are barely affected. The SAXS results were compared with Brunauer-Emmett-Teller results from nitrogen sorption measurements and with mercury intrusion experiments. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: This paper summarizes the principal aims, content and conclusions of a document recently submitted to IUPAC, as a Technical Report, by the IUPAC Working Group on “Liquid intrusion and alternative methods for the characterization of macroporous materials” and to be published in full in Pure and Applied Chemistry. The initial goal of the group was to list, examine and compare the methods presently used to characterize macroporous structures. In addition to mercury porosimetry, the most popular experimental techniques include the intrusion of various non-wetting and wetting liquids, capillary condensation, liquid permeation, imaging and image analysis. The statistical reconstruction of porous materials and the use of macroporous reference materials are also examined. A particular aim is to evaluate the status of mercury porosimetry, since the use of mercury raises a number of safety and environmental issues. The scope and limitations of each method are examined in the context of the scientific and technological requirements and the applicability of some new and unfamiliar methods is also discussed. Finally, an indication is given of the likely direction of future developments in the methodology of macropore characterization. [Copyright &y& Elsevier]